1. Field of the Invention
The present invention relates to an axle driving system which houses an oil reservoir. Oil is fed from the oil reservoir into a chamber housing either a hydraulic non-stage transmission or a differential gear and axles, so that, while the hydraulic non-stage transmission is operating, oil agitated by the differential gear and containing air bubbles does not affect the performance of the hydraulic non-stage transmission.
2. Prior Art
Oil which is stored in a chamber containing a hydraulic non-stage transmission expands as it is heated by the operation of the transmission. The conventional technique of using an oil reservoir tank to accommodate the overflow of oil stored in the chamber is well known. Such techniques include the use of a separate oil reservoir tank, a separate oil reservoir tank made of retractable material, or the provision of a space corresponding to an oil reservoir provided in the transmission housing. The latter is disclosed in Japanese Utility Model Laid-Open No. Hei 2-54964 and in U.S. Pat. No. 4,987,796.
Each of these techniques has its own problems associated therewith. For example, when the reservoir tank is provided in a space in the housing, a long pipe is still required to connect the reservoir tank to the transmission housing. Such an arrangement increases the manufacturing time by increasing the handling of the same. When a retractable material is used in the housing, the manufacturing costs required to erase durability and reliability of the material increase. Further, air disposed within the reservoir tank mixes with the oil when the housing is agitated during use, causing air bubbles to form in the oil. Thus, when the oil is fed into the closed circuit of the hydraulic non-stage transmission, the air bubbles decrease the efficiency of the transmission, resulting in greater noise and lower durability.
In order to eliminate such defects, this inventor has previously disclosed, in pending U.S. patent application Ser. No. 07/917,583, a construction whereby a container for oil including a layer of air disposed above the oil in the container is provided in the housing. The oil can freely interact with oil in the housing, which leaves room for improving the manufacturing cost and structural efficiency of the construction. The present invention is an improvement in this previous construction.